Discovering Gemstones - September Edition
Sapphire, the gemstone of September, brings to mind a beautiful dark blue stone. But in fact, sapphires come in a variety of colours! Corundum, the mineral that sapphire is composed of, can have impurities that change the colour of the rock.
Chromium Pink to red
Iron Yellow to green
Titanium + iron Blue
Vanadium + iron Orange
There is even a type of sapphire called “colour change” sapphire that is an exceptionally rare variety of corundum that can change colour under different light sources. Most colour change sapphire shifts from blue under natural daylight, to violet-purple under incandescent light. But fine, top grade colour change sapphire can turn a range of colours including greenish, yellowish and pinkish. To truly appreciate a colour change sapphire, it should viewed in a variety of light conditions including morning light, afternoon light, fluorescent light and incandescent light.
Sapphires can also appear cloudy or opaque if they have inclusions. An inclusion is any material trapped inside a mineral during its formation that has made its way from the interior to the surface. When titanium oxide forms inclusions in sapphire, called “rutile needles”, it gives the sapphire a characteristics known as “silk” which makes the gem look cloudy or opaque. If the sapphire contains a lot of silk it can be cut into a shape known as a cabochon, which is a rounded, convex gem cut. The intersecting needles of rutile will reflect light off this sapphire as a 6-pointed star which is why it is known as a “star sapphire.”
The most valuable sapphires come from the Kashmir region of India, the Pailin region of Cambodia, Burma and Sri Lanka.